A structure fixed by plural number of bolts that are concentrically arranged is common to hasten respective members which structure a turbomolecular pump. A rotor of turbomolecular pump is rotating at a high speed with several tens of thousands r. p. m. and given the rotor is broken in case while rotating, a strong force (a high impact) in a rotating direction can be transferred to a static site, e.g. a pump casing, due to the rotation energy thereof. Accordingly, a technology to interrupt transferring such strong impact to the side of a vacuum chamber through the pump casing by plastic-deforming a bolt that is fixing the pump to an equipment and a bolt that is fastening a pump casing and a base thereof is known as a technology to absorb the impact. (Referring, for example, to Patent Document 1)